U.S. patent application number 10/414927 was filed with the patent office on 2004-10-21 for optical signal transmission transducer.
Invention is credited to Bhattacharyya, Manoj K., Sharma, Manish.
Application Number | 20040208411 10/414927 |
Document ID | / |
Family ID | 32908323 |
Filed Date | 2004-10-21 |
United States Patent
Application |
20040208411 |
Kind Code |
A1 |
Sharma, Manish ; et
al. |
October 21, 2004 |
Optical signal transmission transducer
Abstract
The invention includes an optical signal transmission
transducer. The optical signal transmission transducer includes a
magnetic tunnel junction. The magnetic tunnel junction can be tuned
to switch states in response to selected frequencies of a magnetic
field. A light source can be modulated based upon states of the
magnetic tunnel junction. An alternate embodiment of the optical
signal transmission transducer includes a light transducer that
generates magnetic sense signals based upon reception of modulated
light signals. The light transducer can be integrated with a
magnetic tunnel junction. The magnetic tunnel junction can be tuned
to switch states in response to selected frequencies of the
magnetic sense signal.
Inventors: |
Sharma, Manish; (Mountain
View, CA) ; Bhattacharyya, Manoj K.; (Cupertino,
CA) |
Correspondence
Address: |
HEWLETT-PACKARD DEVELOPMENT COMPANY
Intellectual Property Administration
P.O. Box 272400
Fort Collins
CO
80527-2400
US
|
Family ID: |
32908323 |
Appl. No.: |
10/414927 |
Filed: |
April 16, 2003 |
Current U.S.
Class: |
385/1 |
Current CPC
Class: |
H04B 10/508
20130101 |
Class at
Publication: |
385/001 |
International
Class: |
G02F 001/01; G02B
006/26 |
Claims
What is claimed:
1. An optical signal transmission transducer: a magnetic tunnel
junction, the magnetic tunnel junction being tuned to switch states
in response to selected frequencies of a magnetic field; and a
light source that is modulated based upon states of the magnetic
tunnel junction.
2. The optical signal transmission transducer of claim 1, wherein
the magnetic tunnel junction and the light source are integrated
within a common substrate.
3. The optical signal transmission transducer of claim 1, further
comprising a magnetic transducer that receives electrical signals
and generates the magnetic field in response to the electrical
signals.
4. The optical signal transmission transducer of claim 1, wherein
the tuning of the magnetic tunnel junction can be adjusted.
5. The optical signal transmission transducer of claim 4, wherein
the tuning of the magnetic tunnel junction can be adjusted by
proper selection of materials of the magnetic tunnel junction.
6. The optical signal transmission transducer of claim 4, wherein
the tuning of the magnetic tunnel junction can be adjusted by
proper selection of physical dimensions of the magnetic tunnel
junction.
7. The optical signal transmission transducer of claim 4, wherein
the tuning of the magnetic tunnel junction can be additionally
adjusted by application of a second magnetic field bias to the
magnetic tunnel junction.
8. The optical signal transmission transducer of claim 3, wherein
the magnetic transducer is responsive enough to generate the
magnetic field at rates the magnetic tunnel junction changes
states.
9. The optical signal transmission transducer of claim 3, wherein
the magnetic transducer comprises an inductive coil.
10. An optical signal transmission transducer: a light transducer
that generates magnetic sense signals based upon reception of
modulated light signals; a magnetic tunnel junction, the magnetic
tunnel junction being tuned to switch states in response to
selected frequencies of the magnetic sense signal.
11. The optical signal transmission transducer of claim 10, further
comprising a magnetic tunnel junction sensor that detects the
states of the magnetic tunnel junction.
12. The optical signal transmission transducer of claim 10, wherein
the light transducer comprises a light sensor and a magnetic
transducer, the light sensor generating electrical signals in
response to the modulated light signals, the magnetic transducer
generating the magnetic sense signals in response to the electrical
signals.
13. The optical signal transmission transducer of claim 10, wherein
the tuning of the magnetic tunnel junction can be adjusted.
14. The optical signal transmission transducer of claim 13, wherein
the tuning of the magnetic tunnel junction can be adjusted by
proper selection of materials of the magnetic tunnel junction.
15. The optical signal transmission transducer of claim 13, wherein
the tuning of the magnetic tunnel junction can be adjusted by
proper selection of physical dimensions of the magnetic tunnel
junction.
16. The optical signal transmission transducer of claim 13, wherein
the tuning of the magnetic tunnel junction can be additionally
adjusted by application of a second magnetic field bias to the
magnetic tunnel junction.
17. An optical transmitter comprising: a plurality of carrier
signal sources for generating a plurality of transmission signals,
each transmission signal including transmission information, each
transmission signal having a unique carrier frequency; a magnetic
transducer for generating a magnetic field in response to the
plurality of transmission signals; a magnetic tunnel junction, the
magnetic tunnel junction being tuned to switch states in response
to selected frequencies of the magnetic field; and a magnetic
tunnel junction sensor for sensing the states of the magnetic
tunnel junction; and a light source that is modulated by the sensed
states of the magnetic tunnel junction.
18. The optical transmitter of claim 17, wherein the tuning of the
magnetic tunnel junction can be adjusted.
19. The optical transmitter of claim 18, wherein the tuning of the
magnetic tunnel junction can be adjusted by proper selection of
materials of the magnetic tunnel junction.
20. The optical transmitter of claim 18, wherein the tuning of the
magnetic tunnel junction can be adjusted by proper selection of
physical dimensions of the magnetic tunnel junction.
21. The optical transmitter of claim 18, wherein the tuning of the
magnetic tunnel junction can be additionally adjusted by
application of a second magnetic field bias to the magnetic tunnel
junction.
22. An optical receiver comprising: means for receiving a plurality
of optical transmission signals, each optical transmission signal
including transmission information, each optical transmission
signal having a unique carrier frequency; a magnetic transducer for
generating a magnetic field in response to the plurality of optical
transmission signals; a magnetic tunnel junction, the magnetic
tunnel junction being tuned to switch states in response to
selected frequencies of the magnetic field; and a magnetic tunnel
junction sensor for sensing the states of the magnetic tunnel
junction.
23. The optical receiver of claim 22, wherein the tuning of the
magnetic tunnel junction can be adjusted.
24. The optical receiver of claim 23, wherein the tuning of the
magnetic tunnel junction can be adjusted by proper selection of
materials of the magnetic tunnel junction.
25. The optical receiver of claim 23, wherein the tuning of the
magnetic tunnel junction can be adjusted by proper selection of
physical dimensions of the magnetic tunnel junction.
26. A method of filtering a plurality of separate frequency
transmission signals, the method comprising: filtering a plurality
of information carrying signals with a magnetic tunnel junction,
the magnetic tunnel junction being tuned to switch states in
response to selected frequencies of the magnetic field; and sensing
the states of the magnetic tunnel junction; and driving a light
source with the sensed states of the magnetic tunnel junction.
27. A method of filtering a plurality of separate frequency
transmission signals, the method comprising: sensing a plurality of
information carrying optical signals; filtering the plurality of
information carrying optical signals with a magnetic tunnel
junction, the magnetic tunnel junction being tuned to switch states
in response to selected frequencies of the magnetic field; and
sensing the states of the magnetic tunnel junction.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to transmission of signals.
More particularly, the invention relates to an optical signal
transmission transducer.
BACKGROUND OF THE INVENTION
[0002] Optical communication systems can include information
signals that are transmitted through an optical transmission
medium. FIG. 1 shows an optical medium 110 (typically an optical
fiber) that can serve as a transmission medium for optical signals.
Generally, a transducer 120 converts electrical signals generated
by a signal source 130 into optical signals. The electrical signals
of the signal source 130 can be modulated by information 140.
Therefore, the optical signals are modulated by the information
140. After transmission through the optical medium 110, the optical
signals can be received by another transducer 150. The transducer
150 can convert the optical signals back to electrical signals.
[0003] Optical communication systems generally include transmission
of multiple carrier signals in which each of the carrier signals is
transmitted at a different transmit frequency. Each individual
transmission signal is typically modulated by an information
signal. Each of the transmission signals can be individually
received, and the information signals can be detected.
[0004] FIG. 2 shows a frequency spectrum of multiple transmission
signals. The transmission signals each include a carrier frequency
FC1, FC2, FC3, FC4. The frequency spectrum allocated to each of the
carrier frequencies is generally referred to as a transmission
channel. The amount of frequency spectrum allocated to each
transmission channel generally determines the amount of information
that can be transmitted through the transmission channel. It is
desirable to utilize as much of the allocated frequency spectrum as
possible.
[0005] The frequency spectrum of FIG. 2 shows transmission signals
210, 220, 230, 240 at the carrier frequencies FC1, FC2, FC3, FC4.
Frequency spectrum adjacent to each of the transmission signals
210, 220, 230, 240 is generally occupied by information that is
modulated onto the transmission signals 210, 220, 230, 240.
Generally, the greater the modulation rate of the information
(typically, the modulation rate is proportional to the amount of
information) the greater the amount of frequency spectrum occupied
by each transmission signal and associated modulation information.
The modulation rate of each transmission signal should not be so
large that the modulation information of one transmission signal
interferes with the modulation information of a neighboring
transmission signal.
[0006] FIG. 3 shows a frequency spectrum of multiple transmission
signals 310, 320, 330, 340 in which information from neighboring
transmission channels overlap. That is, information intended for
transmission through one transmission channel, is unintentionally
transmitted within another transmission channel. For example, the
modulation information of the first transmission signal 310
overlaps with the modulation information of the second transmission
signal 320, as designated 315. The modulation information of the
second transmission signal 320 overlaps with the modulation
information of the third transmission signal 330, as designated
325. The modulation information of the third transmission signal
330 overlaps with the modulation information of the fourth
transmission signal 340, as designated 335.
[0007] The overlap can be due to distortion of the transmission
signals due to components within a transmission system being
non-ideal. The distortion can include noise, spurious signals and
harmonics of transmission signals overlapping with neighboring
transmission signals.
[0008] Information signal channel frequency overlap from one
transmission channel to another transmission channel, introduces
transmission errors. Transmission errors reduce the effectiveness
of a communication system. Additionally, transmission errors can
reduce the transmission bandwidth of a communication.
[0009] It is desirable to provide filtering of optical
communication signals to reduce the amount of frequency spectrum
overlap between transmission signals of the communication
signals.
SUMMARY OF THE INVENTION
[0010] The invention includes an apparatus and method of filtering
of optical communication signals to reduce the amount of frequency
spectrum overlap between transmission signals of the communication
signals.
[0011] An embodiment of the invention includes an optical signal
transmission transducer. The optical signal transmission transducer
includes a magnetic tunnel junction. The magnetic tunnel junction
can be tuned to switch states in response to selected frequencies
of a magnetic field. A light source can be modulated based upon
states of the magnetic tunnel junction.
[0012] An alternate embodiment of the optical signal transmission
transducer includes a light transducer that generates magnetic
sense signals based upon reception of modulated light signals. The
light transducer can be integrated with a magnetic tunnel junction.
The magnetic tunnel junction can be tuned to switch states in
response to selected frequencies of the magnetic sense signal.
[0013] Other aspects and advantages of the present invention will
become apparent from the following detailed description, taken in
conjunction with the accompanying drawings, illustrating by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 shows an optical fiber that can operate as a
transmission path for optical signals.
[0015] FIG. 2 shows a frequency spectrum of several modulated
carrier signals.
[0016] FIG. 3 shows a frequency spectrum of several modulated
carrier signals that include frequency spectrum overlap between
neighboring channels.
[0017] FIG. 4 shows a magnetic tunnel junction sensor.
[0018] FIG. 5 shows waveforms depicting switching of a magnetic
tunnel junction sensor when magnetic switching signals of varying
pulse widths are applied to the magnetic tunnel junction
sensor.
[0019] FIG. 6A shows a magnetic dipole and an applied magnetic
field.
[0020] FIG. 6B shows a sense layer of a magnetic tunnel
junction.
[0021] FIG. 6C shows the precessional motion of a magnetization
vector of a magnetic tunnel junction.
[0022] FIG. 7 shows a plot depicting a probability that a magnetic
tunnel junction will change states when magnetic switching signals
of varying pulse widths are applied to the magnetic tunnel junction
sensor.
[0023] FIG. 8 shows an optical transmitter according to an
embodiment of the invention.
[0024] FIG. 9 shows an optical receiver according to another
embodiment of the invention.
[0025] FIG. 10 shows a frequency response of a magnetic comb filter
according to an embodiment of the invention.
[0026] FIG. 11 is a flow chart that includes acts according to an
embodiment of the invention.
[0027] FIG. 12 shows a circuit schematic of an optical signal
transmission transducer according to another embodiment of the
invention.
[0028] FIG. 13 shows a configuration of a substrate of an optical
signal transmission transducer according to another embodiment of
the invention.
DETAILED DESCRIPTION
[0029] As shown in the drawings for purposes of illustration, the
invention is embodied in an apparatus and method of filtering of
optical communication signals to reduce the amount of frequency
spectrum overlap between transmission signals of the optical
communication signals.
[0030] FIG. 4 shows an embodiment of a magnetic tunnel junction
sensor 400 that includes a reference layer 410, a sense layer 420
and an insulating layer 430.
[0031] The magnetic tunnel junction sensor 400 can be used to
detect the presence of a magnetic field. A magnetic tunnel junction
sensor based on tunneling magneto-resistive devices can include
spin dependent tunneling junctions. The reference layer 410 has a
magnetization orientation that is fixed so as not to rotate in the
presence of an applied magnetic field in a range of interest. The
sense layer 420 has a magnetization that can be oriented in either
one of two directions. If the magnetizations of the reference layer
410 and the sense layer 420 are in the same direction, the
orientation of the spin-dependent tunnel junction is said to be
parallel. If the magnetizations of the reference layer 410 and the
sense layer 420 are in opposite directions, the orientation of the
spin-dependent tunnel junction is said to be anti-parallel. The two
stable orientations, parallel and anti-parallel, may correspond to
logic values of "0" and "1".
[0032] The magnetic orientation of the sense layer 420 is generally
aligned in a direction corresponding to a direction of the last
external magnetic field in the vicinity of the sense layer 420. The
external magnetic field must have enough magnetic strength to alter
the orientation of the sense layer 420 in order for the magnetic
field to be detected.
[0033] A resistance across the magnetic tunnel junction sensor 400
will vary in magnitude depending upon the magnetic orientation of
the sense layer 420 with respect to the magnetic orientation of the
reference layer 410. Typically, if the sense layer 420 has a
magnetic orientation that is in the opposite direction as the
reference layer 410, then the resistance across the magnetic tunnel
junction sensor 400 will be large. If the sense layer 420 has a
magnetic orientation that is in the same direction as the reference
layer 410, then the resistance across the magnetic tunnel junction
sensor 400 will be less. Therefore, the resistance across the
magnetic tunnel junction sensor 400 can be used to sense the
direction of a magnetic field because the direction of the magnetic
field determines the magnetic orientation of the sense layer 420
with respect to the reference layer 410, and therefore, the
resistance across the magnetic sensor 400.
[0034] The reference layer 410 and the sense layer 420 can be made
of a ferromagnetic material. The reference layer 410 can be
implemented with a magnetically soft reference layer, or with a
magnetically pinned layer.
[0035] If the magnetization of the sense layer 420 and the
reference layer 410 of the magnetic tunnel junction sensor 400 are
in the same direction, the orientation of the magnetic tunnel
junction sensor 400 can be referred to as being "parallel." If the
magnetization of the sense layer 420 and the reference layer 410 of
the magnetic tunnel junction sensor are in opposite directions, the
orientation of the magnetic tunnel junction sensor can be referred
to as being "anti-parallel." The two orientations, parallel and
anti-parallel, can correspond to magnetic sensor states of low or
high resistance.
[0036] The insulating tunnel barrier 430 allows quantum mechanical
tunneling to occur between the reference layer 410 and the sense
layer 420. The tunneling is electron spin dependent, causing the
resistance of the magnetic tunnel junction sensor to be a function
of the relative orientations of the magnetization directions of the
reference layer 410 and the sense layer 420. The presence of a
magnetic field can be detected by establishing the magnetization
orientations of the reference layer 410 and the sense layer
420.
[0037] The resistance of the magnetic tunnel junction sensor 400 is
a first value (R) if the magnetization orientation of the magnetic
tunnel junction sensor 400 is parallel and a second value (R+delta)
if the magnetization orientation is anti-parallel. The invention,
however, is not limited to the magnetization orientation of the two
layers, or to just two layers.
[0038] The insulating tunnel barrier 430 can be made of aluminum
oxide, silicon dioxide, tantalum oxide, silicon nitride, aluminum
nitride, or magnesium oxide. However, other dielectrics and certain
semiconductor materials may also be used for the insulating tunnel
barrier 430. The thickness of the insulating tunnel barriers 430
may range from about 0.5 nanometers to about three nanometers.
However, the invention is not limited to this range.
[0039] The sense layer 420 may be made of a ferromagnetic material.
Both the sense layer 420, and the reference layer 410 can be
implemented as a synthetic ferrimagnet (SF), also referred to as an
artificial antiferromagnet.
[0040] The sense layer 430 of the tunnel junction sensor 400 will
generally align in a direction that corresponds with a direction of
an externally applied magnetic field.
[0041] FIG. 5 shows waveforms depicting switching of a magnetic
tunnel junction sensor when magnetic switching signals of varying
pulse widths are applied to the magnetic tunnel junction sensor. A
first waveform 510 depicts the state of the magnetic tunnel
junction sensor when a magnetic field having a pulse width of 125
ps is applied. A second waveform 520 depicts the state of the
magnetic tunnel junction sensor when a magnetic field having a
pulse width of 250 ps is applied. A third waveform 530 depicts the
state of the magnetic tunnel junction sensor when a magnetic field
having a pulse width of 350 ps is applied. The amplitude of the
magnetic field applied is 200 Oe for each of the waveforms.
[0042] The waveforms show that the magnetic tunnel junction sensor
is more likely to switch states for particular pulse widths rather
than others. For example, the waveforms of FIG. 5 show the magnetic
tunnel junction sensor switching states of a pulse width of 250
ps.
[0043] Due to a switching characteristic of magnetic tunnel
junctions (generally referred to as precessional switching),
magnetic tunnel junctions will switch for pulses of particular
pulse widths, but not for other pulse widths. Typically, there are
many selective ranges of pulse widths that cause the magnetic
tunnel junction to switch. The pulse widths can be equated to
periods of sinusoidal waveforms. Sinusoidal waveforms that include
"on" period equivalent to the selected pulse widths can cause the
magnetic tunnel junction to change states. This time/frequency
selective characteristic of magnetic tunnel junctions allows the
magnetic tunnel junctions to be used as a selective switch or
filter.
[0044] The selective time/frequency switching characteristics of
magnetic tunnel junctions can be experimentally or computationally
determined. Therefore, the magnetic tunnel junctions can be tuned
to selectively pass signals that include particular
frequencies.
[0045] Many applications exist that can utilize the selective
signal frequency pass bands of the invention. The descriptions
provided here of signal transmitters and signal receivers that can
utilize a frequency comb filter as provided by the invention are
merely examples of useful applications of the invention. The
invention can be utilized in many different applications where high
frequency selective filtering is beneficial.
[0046] Precessional Switching
[0047] Precessional switching is a phenomenon that can be used to
describe the transitional regions of the switching curves of FIG.
5. Precessional switching will first be described as applied to a
single magnetic dipole, and then as applied to a magnetic tunnel
junction of the invention.
[0048] FIG. 6A shows a magnetic moment m of a single magnetic
dipole. If a magnetic field Heff is applied to the magnetic dipole,
the magnetic dipole will experience precession about an axis of the
applied magnetic field Heff as the magnetic dipole attempts to
align with the applied magnetic field Heff. The precession is
depicted by a circular rotation 610 about the axis of the applied
magnetic field Heff.
[0049] As shown in FIG. 6A, the axis of the applied magnetic field
is at an angle A with respect to the depicted z-axis, and the
magnetic moment of the dipole is at an angle B with respect to the
depicted z-axis.
[0050] The precession can be calculated by an equation of motion as
given by:
[0051] (1/.gamma.)(dm/dt)=m.times.Heff, where m is the magnetic
moment of the dipole, and .gamma. is the well known gyromagnetic
ratio. A standard value of .gamma. can be given as
1.76.times.10.sup.7 Oe.sup.-1 s.sup.-1.
[0052] The estimated precession of the magnetic tunnel junctions of
the invention, further include damping and exchange interactions
between a large number of dipoles that are used to model the sense
layer of the magnetic tunnel junction. Once these factors are
included, and the calculations summed for all dipoles of a
ferromagnetic bit of a magnetic tunnel junction, a final equation
of motion generally termed the Landau-Lifshitz-Gilbert equation can
be used to determine the precession of the magnetic tunnel
junction. This equation of motion can be represented as:
[0053]
(dM/dt)=-.gamma.(M.times.(.delta.w/.delta.M)-(.alpha./M)(M.times.(d-
M/dt)); where M is the magnetization vector, .gamma. is the
gyromagnetic ratio, .alpha. is a damping ratio, (.delta.w/.delta.M)
is a total derivative of the energy density with magnetization
Heff.
[0054] FIG. 6B shows a sense layer of a magnetic tunnel junction
and the corresponding x-axis, y-axis and z-axis.
[0055] FIG. 6C shows an example of the precession of the
magnetization M (also referred to as the net magnetic moment) of
the sense layer as calculated by the previously described
Landau-Lifshitz-Gilbert equation.
[0056] As shown in FIG. 6C, initially, the magnetization vector M
of the magnetic tunnel junction is oriented along the x-axis. Once
the magnetic field Heff is applied, the magnetization vector M
begins to rotate and change direction according to the line 620 as
the magnetization vector M attempts to align with the magnetic
field Heff. The speed at which the magnetization vector M changes
directions is dependent upon the damping elements of the motion,
and geometry and materials of the magnetic tunnel junction. The
motion can be simulated by the Landau-Lifshitz-Gilbert equation
using micromagnetic models in the dynamic domain (that is, time
scales of less than 1 ns).
[0057] For the invention, the precession is modeled to provide
predictions of the exact amplitude and duration of a magnetic pulse
required to cause the magnetization vector of a magnetic tunnel
junction to switch. The duration and amplitude of the applied
magnetic pulse are varied to identify specific frequencies at which
the magnetic tunnel junction will switch. The selective switching
frequencies are used to provide the filter effects of the
invention.
[0058] FIG. 7 shows a plot depicting a probability that a magnetic
tunnel junction will change states when magnetic switching signals
of varying pulse widths are applied to the magnetic tunnel junction
sensor. A first peak 710 occurs for a pulse width of 150 ps. A
second peak 720 occurs for a pulse width of 290 ps. A third peak
730 occurs for a pulse width of 430 ps.
[0059] All of the pulses include an amplitude of 200 Oe. The pulse
width may vary for different pulse amplitudes.
[0060] According to the plot, pulse widths of 150 ps, 290 ps and
430 ps are more likely to cause the magnetic tunnel junction to
change states. This plot can be used to determine the pass band
frequencies of a comb filter formed by the magnetic tunnel
junction. Generally, signals will be passed that have a frequency
that includes a time period that is equivalent to the pulse widths
of the pulses that cause the tunnel magnetic junction to
switch.
[0061] For example, if a signal that includes an amplitude of
greater than 200 Oe for a duration of 150 ps, will cause the
magnetic tunnel junction to switch states, and the signal will not
be filtered (that is, it will pass through) by the magnetic tunnel
junction.
[0062] The pass bands of the magnetic comb filter of the invention
can be tuned. That is, the pass bands of the comb filter can be
tuned. The tuning can be accomplished by manipulating the materials
within the MTJ, or by manipulating the physical characteristics of
the magnetic tunnel junction. The actual tuning frequencies can be
simulated and experimentally determined.
[0063] Additionally, the pass bands of the comb filter of the
invention can be tuned on the fly. That is, a magnetic field can be
applied orthogonal (that is, in a different direction) to the
direction of magnetization of the reference and sense layers. This
applied field alters the pulse widths required to cause the
magnetic tunnel junction to switch. Therefore, the frequencies of
the pass-bands of the comb filter are altered. The effects of the
magnetic fields applied in an orthogonal direction can be simulated
and experimentally determined. The pass band frequencies of the
magnetic tunnel junction can be determined either experimentally,
through simulation, or through a combination of both.
[0064] FIG. 8 shows an optical signal transmission transducer 800
according to an embodiment of the invention. The optical signal
transmission transducer 800 can receive an electronic signal (the
electronic signal can include several different signals in which
each signal includes a separate carrier frequency) and a light
source is modulated by a comb filtered version of the electronic
signal.
[0065] This embodiment of the optical signal transmission
transducer 800 includes a transducer 810 that can receive the
electronic signal and generate a magnetic field having an intensity
proportional to the electronic signal. The transducer should be
operable at frequencies that are included within the electronic
signal.
[0066] This embodiment of the optical signal transmission
transducer 800 further includes a magnetic tunnel junction 820. The
magnetic tunnel junction 820 can be tuned to switch states in
response to selected frequencies of the magnetic field. The
material and physical parameters of the magnetic tunnel junction
820 generally define the frequency component filtering of the
magnetic tunnel junction 820, and therefore, the filtering of the
optical signal transmission transducer 800.
[0067] A magnetic tunnel junction sensor 830 can sense the states
of the magnetic tunnel junction 820. As previously described, the
states of the magnetic tunnel junction 820 can be determined by
sensing a resistance across the magnetic tunnel junction 820.
[0068] As previously described, only certain frequency components
of the electronic signal will pass through the magnetic tunnel
junction 820. Additionally, as previously stated, the frequency
components that pass through the magnetic tunnel junction 820 can
be tuned either by design, or while in operation.
[0069] A light source 840 can be electronically connected to the
magnetic tunnel junction sensor 830. The light source can be
modulated based upon states of the magnetic tunnel junction 820.
The light source 840 can include a light emitting diode, or a
laser, in which an intensity of light emitted by the diode or the
laser can be electronically controlled.
[0070] FIG. 9 shows an optical signal transmission transducer 900
according to another embodiment of the invention. Generally, the
optical signal transmission transducer 900 receives an optical
signal, comb filters the optical signal, and generates an
electronic equivalent of the received optical signal. The received
optical signal can include many different information signals in
which each information signal includes a separate carrier
frequency.
[0071] The optical signal transmission transducer 900 includes a
transducer 910 that converts the received optical signal into a
magnetic field in which an intensity of the magnetic field is
dependent upon the optical signal. The transducer 910 can include
sub-transducers that convert the optical signal into an electronic
signal, and then convert the electronic signal into an
electromagnetic signal.
[0072] The optical signal transmission transducer 900 further
includes a magnetic tunnel junction 920. The magnetic tunnel
junction 920 can be tuned to switch states in response to selected
frequencies of the magnetic field. The material and physical
parameters of the magnetic tunnel junction 920 generally define the
frequency component filtering of the magnetic tunnel junction 920,
and therefore, the filtering of the optical signal transmission
transducer 900.
[0073] A magnetic tunnel junction sensor 930 can sense the states
of the magnetic tunnel junction 920. As previously described, the
states of the magnetic tunnel junction 920 can be determined by
sensing a resistance across the magnetic tunnel junction 920.
[0074] As previously described, only certain frequency components
of the electronic signal will pass through the magnetic tunnel
junction 920. Additionally, as previously stated, the frequency
components that pass through the magnetic tunnel junction 920 can
be tuned either by design, or while in operation.
[0075] The embodiment of FIG. 9 further includes a buffer amplifier
940.
[0076] FIG. 10 shows an ideal frequency response of a magnetic comb
filter according to an embodiment of the invention. The frequency
response allows particular frequency components to pass through the
comb filter, while filtering or attenuating other frequency
components. More precisely, the frequency response includes
frequency pass bands 1010, 1020, 1030, 1040. The invention provides
selective filtering of electromagnetic signals. As previously
described, the tuning of the pass bands of the filtering provided
by the invention can be tuned. Additionally, the pass bands can be
actively tuned in real-time by applying additional magnetic fields
to the magnetic tunnel junctions of the invention. Generally, the
additional magnetic fields are applied in an a direction that is
orthogonal to the magnetic field generated by the applied signals
to be filtered.
[0077] As previously described, the selective time/frequency
switching characteristics of magnetic tunnel junctions can be
experimentally or computationally determined. Therefore, the
magnetic tunnel junctions can be tuned to selectively pass signals
that include particular frequencies.
[0078] Many applications exist that can utilize the selective
signal frequency pass bands of the invention. The descriptions
provided here of signal transmitters and signal receivers that can
utilize a frequency comb filter as provided by the invention are
merely examples of useful applications of the invention. The
invention can be utilized in many different applications where high
frequency selective filtering is beneficial.
[0079] FIG. 11A is a flow chart that includes act according to an
embodiment of the invention. This embodiment includes a method of
filtering a plurality of separate frequency transmission
signals.
[0080] A first step 1105 includes filtering a plurality of
information carrying signals with a magnetic tunnel junction, the
magnetic tunnel junction being tuned to switch states in response
to selected frequencies of the magnetic field.
[0081] A second step 1110 includes sensing the states of the
magnetic tunnel junction.
[0082] A third step 1115 includes driving a light source with the
sensed states of the magnetic tunnel junction.
[0083] FIG. 11B is a flow chart that includes act according to
another embodiment of the invention. This embodiment includes a
method of filtering a plurality of separate frequency transmission
signals.
[0084] A first step 1120 includes sensing a plurality of
information carrying optical signals.
[0085] A second step 1125 includes filtering the plurality of
information carrying optical signals with a magnetic tunnel
junction, the magnetic tunnel junction being tuned to switch states
in response to selected frequencies of the magnetic field.
[0086] A third step 1130 includes sensing the states of the
magnetic tunnel junction.
[0087] FIG. 12 shows a circuit schematic of an optical signal
transmission transducer according to another embodiment of the
invention. This embodiment includes a light emitting diode (LED)
1210 that emits light. The amount of light emitted from the LED
1210 can be dependent upon a bias current flowing through the LED
1210.
[0088] The intensity of the light emitted by the LED 1210 can be
controlled by a resistance of a magnetic tunnel junction 1220. As
previously described, the resistance of the tunnel magnetic
junction 1220 is dependent upon the state of the tunnel magnetic
junction 1220. Therefore, the states of the magnetic tunnel
junction 1220 control the intensity of the light emitted from the
LED 1210. The states of the tunnel magnetic junction 1220 are
determined by the application of a magnetic field Happ.
[0089] The embodiment shown in FIG. 12 further includes a bias
transistor 1230 and a bias controller 1240. The bias controller
1240 can be configured so that the bias current flowing through the
LED 1210 is dependent upon the resistance of the tunnel magnetic
junction 1220, and therefore, the state of the tunnel magnetic
junction 1220.
[0090] The embodiment of FIG. 12 is merely an example of circuit in
which the intensity of a light source is modulated based upon the
state of a magnetic tunnel junction. Many other possible circuits
that provide for modulation of a light source depending upon the
resistance of a magnetic tunnel junction are possible.
[0091] An alternate embodiment includes the light emitting source
being a laser diode such as a vertical cavity surface emitting
laser (VCSEL). The invention can also use other modulated light
sources.
[0092] FIG. 13 shows a configuration of a substrate 1310 of an
optical signal transmission transducer according to another
embodiment of the invention. The substrate includes a controlling
transistor 1320, a magnetic tunnel junction 1330 and a controllable
light emitting device 1340.
[0093] The controlling transistor 1320, the magnetic tunnel
junction 1330 and the controllable light emitting device 1340 can
be electrically connected through conductive lines 1352, 1354,
1356.
[0094] The controlling transistor 1320 can be formed in the
substrate 1310, and include a source 1312, a drain 1314 and a
poly-Si gate 1316. The magnetic tunnel junction 1330 can be formed
over the controlling transistor 1320. The controlling transistor
1320 can be electrically connected to a light emitting device
1340.
[0095] Standard semiconductor processing steps can be used to form
the controlling transistor 1320.
[0096] The light emitting device 1340 can include a PIN diode that
includes a p-contact 1342, a p-AlGaAs layer 1343, an i-GaAs layer
1344 an n-AlGaAs layer 1445 and an n-contact 1346.
[0097] Standard semiconductor processing steps can be used to form
the light emitting device 1340.
[0098] Standard semiconductor processing steps can be used to form
the conductive lines 1352, 1354, 1356. Similar semiconductor
processing steps can be used to form the conductive layers of the
MTJ 1330.
[0099] The embodiment of FIG. 13 provides an integrated MTJ 1330
and light emitting device 1340 that can provide selective comb
filtering. As previously described, the filtering is dependent upon
the materials and physical characteristics of the MTJ 1330.
[0100] Although specific embodiments of the invention have been
described and illustrated, the invention is not to be limited to
the specific forms or arrangements of parts so described and
illustrated. The invention is limited only by the appended
claims.
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